The present invention relates to electrochemically measuring the concentration of fluid contaminants.
Measurements of the type to which the invention pertains is usually carried out by means of a measuring cell which contains two electrodes made of similar material and being in contact with an electrolyte. One of the electrodes is arranged and configured so that the fluid under examination can reach the phase boundary of the electrode and the electrolyte. An electrical signal can be taken from between the electrodes and information concerning the concentration of a particular component in that fluid can be derived from that signal.
An immediate problem arises involving cells of this type in that the cell may readily respond also to other components in the sample gas. In order to eliminate such a non-selectivity of the device one has used special filters which eliminate those additional components but permit passage of the component or contaminant to be detected. Such selective filters exhibit the drawback that inevitably they block also some of the compound to be measured. Moreover, such filter will rather rapidly saturate and have to be exchanged so that the maintenance of these devices is correspondingly extensive.
The German printed patent application No. 2,436,261 discloses an electrochemical measuring cell for various gaseous substances wherein blocking substances in the electorlyte impede any reaction with undesired components. The measuring gas flows past one of the two electrodes in the cell. The two electrodes are made of similar material.
The German printed patent application No. 2,435,813 discloses a measuring device whose selectivity results from an arrangement of different cells which respond differently to different compounds. The various electrical outputs are interconnected by a resistance network which produces a signal that in fact represents the concentration of the desired compound only, while the signals representing other compounds are suppressed.